Investigations on the Reaction of C3 and C6 α-Dicarbonyl Compounds with Hydroxytyrosol and Related Compounds under Competitive Conditions

Contents of ɑ-dicarbonyl compounds in commercial black tea and affected by the processing

The species and contents of ɑ-dicarbonyls in commercial black tea were examined, along with the effects of the manufacturing process and drying temperature on the formation of ɑ-dicarbonyls. Ten ɑ-dicarbonyls were quantified in commercial and in-process black tea samples by using UPLC-MS/MS and their derived quinoxalines. The ɑ-dicarbonyls content in commercial black tea decreased significantly (p < 0.05) in the following order: 3-deoxyglucosone > glucosone > 3-deoxypentosone = threosone > galactosone ≥ methylglyoxal = glyoxal ≥ 3-deoxygalactosone = 3-deoxythreosone = diacetyl. Except for 3-deoxyglucosone and 3-deoxygalactosone, a further eight ɑ-dicarbonyls were identified in all manufacturing steps of black tea. Except for the drying step, the rolling and fermenting played important roles in the formation of ɑ-dicarbonyls. The total contents of ɑ-dicarbonyls in black tea infusion ranged from 16.48 to 75.32 μg/g based on our detected ten ɑ-dicarbonyls.

α-Dicarbonyl compounds in food products: Comprehensively understanding their occurrence, analysis, and control

α-Dicarbonyl compounds (α-DCs) are readily produced during the heating and storage of foods, mainly through the Maillard reaction, caramelization, lipid-peroxidation, and enzymatic reaction. They contribute to both the organoleptic properties (i.e., aroma, taste, and color) and deterioration of foods and are potential indicators of food quality. α-DCs are also important precursors to hazardous substances, such as acrylamide, furan, advanced lipoxidation end products, and advanced glycation end products, which are genotoxic, neurotoxic, and linked to several diseases. Recent studies have indicated that dietary α-DCs can elevate plasma α-DC levels and lead to "dicarbonyl stress." To accurately assess their health risks, quantifying α-DCs in food products is crucial. Considering their low volatility, inability to absorb ultraviolet light, and high reactivity, the analysis of α-DCs in complex food systems is a challenge. In this review, we comprehensively cover the development of scientific approaches, from extraction, enrichment, and derivatization, to sophisticated detection techniques, which are necessary for quantifying α-DCs in different foods. Exposure to α-DCs is inevitable because they exist in most foods. Recently, novel strategies for reducing α-DC levels in foods have become a hot research topic. These strategies include the use of new processing technologies, formula modification, and supplementation with α-DC scavengers (e.g., phenolic compounds). For each strategy, it is important to consider the potential mechanisms underlying the formation and removal of process contaminants. Future studies are needed to develop techniques to control α-DC formation during food processing, and standardized approaches are needed to quantify and compare α-DCs in different foods.

Reduction of 3-Deoxyglucosone by Epigallocatechin Gallate Results Partially from an Addition Reaction: The Possible Mechanism of Decreased 5-Hydroxymethylfurfural in Epigallocatechin Gallate-Treated Black Garlic

5-Hydroxymethylfurfural (5-HMF) is a harmful substance generated during the processing of black garlic. Our previous research demonstrated that impregnation of black garlic with epigallocatechin gallate (EGCG) could reduce the formation of 5-HMF. However, there is still a lack of relevant research on the mechanism and structural identification of EGCG inhibiting the production of 5-HMF. In this study, an intermediate product of 5-HMF, 3-deoxyglucosone (3-DG), was found to be decreased in black garlic during the aging process, and impregnation with EGCG for 24 h further reduced the formation of 3-DG by approximately 60% in black garlic compared with that in the untreated control. The aging-mimicking reaction system of 3-DG + EGCG was employed to determine whether the reduction of 3-DG was the underlying mechanism of decreased 5-HMF formation in EGCG-treated black garlic. The results showed that EGCG accelerated the decrease of 3-DG and further attenuated 5-HMF formation, which may be caused by an additional reaction with 3-DG, as evidenced by LC-MS/MS analysis. In conclusion, this study provides new insights regarding the role of EGCG in blocking 5-HMF formation.

Kinetics of α‑dicarbonyl compounds formation in glucose-glutamic acid model of Maillard reaction

As a potential health hazard, α-dicarbonyl compounds have been detected in the thermally processed foods. In order to investigate the formation kinetics of α-dicarbonyl compounds, liquid chromatography-electrospray tandem mass spectrometry was employed to determine the content of α-dicarbonyl compounds in glucose-only and glucose-glutamic acid (glucose-Glu) thermal reaction models. The 3-deoxyglucosone content was significantly higher than 6 α-dicarbonyl compounds at 90-110℃, 0-6 hr in the two tested systems. The glutamic acid promoted the content accumulation of 1-deoxyglucosone, diacetyl, methylglyoxal, and glyoxal, whereas inhibited the content of 3-deoxyglucosone and 3,4-dideoxyglucosone. Three-fifths of the tested compounds content increased linearly with time increasing, but in glucose-only system, the 1-deoxyglucosone content increased logarithmically at 95-110℃ over reaction time. The formation of glucose (100-110℃, glucose-only and glucose-Glu), 5-hydroxymethylfurfural (100-110℃, glucose-only), 1-deoxyglucose (105-110℃, glucose-Glu), 3,4-dideoxyglucosone (110℃, glucose-Glu), glyoxal (95-110℃, glucose-Glu) and diacetyl (90-95℃, glucose-Glu) could be well fitted by exponential equation. Shortening the heating time and reducing heating temperature (except glyoxal in glucose-only system) were the effective methods to decrease α-dicarbonyl compounds content in the two tested systems. Additionally, high temperature could also reduce α-dicarbonyl compounds content, such as 3-deoxyglucosone (≥110℃, glucose-only), 1-deoxyglucosone (≥110℃, glucose-only), glucosone (≥110℃, glucose-only; ≥100℃, glucose-Glu), methyloxyl (≥110℃, glucose-only; ≥100℃, glucose-Glu), diacetyl (≥110℃, glucose-only), and glyoxal (≥100℃, glucose-Glu).

Trapping of Carbonyl Compounds by Epicatechin: Reaction Kinetics and Identification of Epicatechin Adducts in Stored UHT Milk

The kinetics of the reaction between epicatechin and various carbonyl compounds typically formed in cooked and stored foods were evaluated in model systems at pH 7.4 and 37 °C, and the corresponding reaction products in stored ultrahigh temperature (UHT) milk-added epicatechin were identified by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The rate constants for the reactions of carbonyl compounds with epicatechin decreased in the following the order: methylglyoxal; 1.6 ± 0.2 M^-1 s^-1 > glyoxal; (5.9 ± 0.3) × 10^-2 M^-1 s^-1 ≥ 5-(hydroxymethyl)furfural; (4.0 ± 0.2) × 10^-2 M^-1 s^-1 ≥ acetaldehyde; (2.6 ± 0.3) × 10^-2 M^-1 s^-1 ≥ phenylacetaldehyde; (2.1 ± 0.2) × 10^-2 M^-1 s^-1 ≥ furfural; (4.3 ± 0.1) × 10^-3 M^-1 s^-1 > 2-methylbutanal and 3-methylbutanal; ∼0 M^-1 s^-1. Reaction products generated by epicatechin and methylglyoxal, glyoxal, 5-(hydroxymethyl)furfural, and acetaldehyde were detected in UHT milk samples by incubating milk samples with epicatechin at 37 °C for 24 h. The lack of reaction between epicatechin and phenylacetaldehyde, furfural, 2-methylbutanal, and 3-methylbutanal in stored UHT milk may be due to their slow reaction rates or low concentration in stored UHT milk. It is demonstrated that epicatechin traps 5-(hydroxymethyl)furfural, acetaldehyde, glyoxal, and methylglyoxal and may thereby reduce off-flavor formation in UHT milk during storage both by trapping of precursors (methylglyoxal and glyoxal) for off-flavor formation and by direct trapping of off-flavors.

Spray-dried olive mill wastewater reduces Maillard reaction in cookies model system

The network of the Maillard reaction can be influenced by the presence of polyphenols. In this paper, we evaluated the ability of secoiridoids to interact with asparagine and lysine tuning the formation of dietary advanced glycation end-products (d-AGEs), dicarbonyls and acrylamide. Olive oil mill wastewater polyphenol powders (OMWP) were added to glucose and lysine or asparagine in silica model systems to mimic water activity present in cookies. Results revealed that acrylamide, Amadori compounds and N-ε-carboxyethyllysine (CEL) were reduced to 50%, after 13 min at 180 °C; for the reduction of N-ε-carboxymethyllysine (CML), secoiridoids were effective only in model systems with the addition of acacia fiber and maltodextrin as coating agents. In cookies, OMWP at three different concentrations decreased the concentration of protein bound Amadori compounds, CML, CEL and dicarbonyls. Acrylamide and 5-hydroxymethylfurfural were reduced to 60% and 76% respectively, highlighting the ability of secoiridoids-based functional ingredients in controlling d-AGEs formation.

Comparison of Differences of α-Dicarbonyl Compounds between Naturally Matured and Artificially Heated Acacia Honey: Their Application to Determine Honey Quality

α-Dicarbonyl compounds (α-DCs) are a major class of intermediates generated during Maillard reactions. They can serve as chemical markers of thermal processing and storage of sugar-rich foods. To distinguish between naturally matured acacia honey (NMAH) and artificially heated acacia honey (AHAH), we purified 12 major α-DCs quinoxaline derivatives to investigate the effects of temperature during heat treatment and storage on their accumulation in acacia honey. Nine of the 12 α-dicarbonyl compounds were found in acacia honey samples, and their contents varied depending on processing and storage conditions. Among them, the contents of 3-deoxyglucosulose (3-DG), 1,4-dideoxyglucosone (1,4-DDG), and 1-deoxyglucosone (1-DG) increased commensurately with heat. 3-DG content ranged from 103.7 to 146.6 mg/kg in NMAH and 572.4-1371.2 mg/kg in AHAH. Given the abundance and stability of 3-DG following heat treatment and storage, this compound can potentially serve as a reliable marker for distinguishing between NMAH and AHAH.

Mitigation of 3-deoxyglucosone and 5-hydroxymethylfurfural in brown fermented milk via an alternative browning process based on the hydrolysis of endogenous lactose

During the conventional production of brown fermented milk (BFM), unhealthy substances (3-deoxyglucosone (3-DG), methylglyoxal (MGO), and 5-hydroxymethylfurfural (HMF)) are generated during the Maillard browning step. Here, an alternative browning process based on the hydrolysis of endogenous lactose was established. Compared with the conventional process, 3-DG and HMF were decreased by 5.91 mg kg-1 and 0.39 mg kg-1 in the brown milk base under the alternative browning process, and thereafter, 3-DG and HMF were decreased by 54.5% and 65.0% in BFM. Investigation into the formation of 3-DG, MGO, and HMF in different chemical models showed that different sugars lead to different Maillard reaction products and browning rates, contributing to the mitigation of 3-DG and HMF. Apart from the mitigation of unhealthy Maillard compounds, hydrolyzing lactose and avoiding the addition of external glucose make the alternative browning process a theoretical and practical basis for improving the quality and safety of BFM.

Formation and Alterations of the Potentially Harmful Maillard Reaction Products during the Production and Storage of Brown Fermented Milk

To improve the quality and safety of brown fermented milk (BFM), the formation and alterations of potentially harmful Maillard reaction products (MRPs), including 3-deoxyglucosone (3-DG), methylglyoxal (MGO), 5-(hydroxymethyl)-2-furfural (HMF), acrylamide and flavour components were investigated during the browning, fermentation and commercial storage. MRPs were shown to be produced mainly during the browning stage. The levels of different substances varied during the fermentation and commercial storage stage. The proportion and type of carboxylic acids in the flavour components significantly increased during the fermentation stage. Browning index of milk during the browning stage was shown to be positively associated with the 3-DG (Pearson's r = 0.9632), MGO (Pearson's r = 0.9915), HMF (Pearson's r = 0.9772), and acrylamide (Pearson's r = 0.7910) levels and the total percentage of the flavour components from four different categories (Pearson's r = 0.7407). Changes in physicochemical properties of BFM during production not only contribute to predict the formation of potentially unhealthy MRPs, but also Lactobacillus species used for the fermentation should be carefully selected to improve the quality of this product.

Structure-Activity Relationship (SAR) of Phenolics for the Inhibition of 2-Phenylethylamine Formation in Model Systems Involving Phenylalanine and the 13-Hydroperoxide of Linoleic Acid

Lipid hydroperoxides have been shown to produce amino acid decarboxylations. Because thermal decomposition of lipid hydroperoxides produces free radicals and reactive carbonyls, and phenolic compounds have been shown to scavenger both of them, phenolics are expected to inhibit these reactions and this protection should depend on the structures of the involved phenolics. In this study, the effect of a wide array of phenolics and their mixtures on 2-phenylethylamine formation by phenylalanine degradation in the presence of the 13-hydroperoxide of linoleic acid (LOOH) was studied. LOOH increased considerably the formation of the amine, and phenolics mostly exhibiting an inhibitory role that depended on their structure. Thus, 1,3-diphenols decreased the formation of 2-phenylethylamine because of their carbonyl trapping abilities. In contrast, the inhibition of 1,2- and 1,4-diphenols was lower because they could not trap the reactive carbonyls produced by LOOH decomposition. In addition, their free radical scavenging was likely accompanied by the formation of quinones, which acted as reactive carbonyls. The function of all other phenolics could be calculated by adding the individual functions of the different diphenols present in their structures. In fact, experimental values obtained for both mixtures of phenolics and complex phenolics correlated well with the calculated values obtained from their constituting diphenols. All of these results suggest that, when the reaction mechanisms are known, it is possible to predict the behavior of complex phenolics on the basis of their structure.

Maillard Proteomics: Opening New Pages

Protein glycation is a ubiquitous non-enzymatic post-translational modification, formed by reaction of protein amino and guanidino groups with carbonyl compounds, presumably reducing sugars and α-dicarbonyls. Resulting advanced glycation end products (AGEs) represent a highly heterogeneous group of compounds, deleterious in mammals due to their pro-inflammatory effect, and impact in pathogenesis of diabetes mellitus, Alzheimer's disease and ageing. The body of information on the mechanisms and pathways of AGE formation, acquired during the last decades, clearly indicates a certain site-specificity of glycation. It makes characterization of individual glycation sites a critical pre-requisite for understanding in vivo mechanisms of AGE formation and developing adequate nutritional and therapeutic approaches to reduce it in humans. In this context, proteomics is the methodology of choice to address site-specific molecular changes related to protein glycation. Therefore, here we summarize the methods of Maillard proteomics, specifically focusing on the techniques providing comprehensive structural and quantitative characterization of glycated proteome. Further, we address the novel break-through areas, recently established in the field of Maillard research, i.e., in vitro models based on synthetic peptides, site-based diagnostics of metabolism-related diseases (e.g., diabetes mellitus), proteomics of anti-glycative defense, and dynamics of plant glycated proteome during ageing and response to environmental stress.

Green Tea Polyphenols Decrease Strecker Aldehydes and Bind to Proteins in Lactose-Hydrolyzed UHT Milk

The effect of epigallocatechin gallate enriched green tea extract (GTE) on flavor, Maillard reactions and protein modifications in lactose-hydrolyzed (LH) ultrahigh temperature (UHT) processed milk was examined during storage at 40 °C for up to 42 days. Addition of GTE inhibited the formation of Strecker aldehydes by up to 95% compared to control milk, and the effect was similar when GTE was added either before or after UHT treatment. Release of free amino acids, caused by proteolysis, during storage was also decreased in GTE-added milk either before or after UHT treatment compared to control milk. Binding of polyphenols to milk proteins was observed in both fresh and stored milk samples. The inhibition of Strecker aldehyde formation by GTE may be explained by two different mechanisms; inhibition of proteolysis during storage by GTE or binding of amino acids and proteins to the GTE polyphenols.

Food-derived 1,2-dicarbonyl compounds and their role in diseases

Reactive 1,2-dicarbonyl compounds (DCs) are generated from carbohydrates during food processing and storage and under physiological conditions. In the recent decades, much knowledge has been gained concerning the chemical formation pathways and the role of DCs in food and physiological systems. DCs are formed mainly by dehydration and redox reactions and have a strong impact on the palatability of food, because they participate in aroma and color formation. However, they are precursors of advanced glycation end products (AGEs), and cytotoxic effects of several DCs have been reported. The most abundant DCs in food are 3-deoxyglucosone, 3-deoxygalactosone, and glucosone, predominating over methylglyoxal, glyoxal, and 3,4-dideoxyglucosone-3-ene. The availability for absorption of individual DCs is influenced by the release from the food matrix during digestion and by their reactivity towards constituents of intestinal fluids. Some recent works suggest formation of DCs from dietary sugars after their absorption, and others indicate that certain food constituents may scavenge endogenously formed DCs. First works on the interplay between dietary DCs and diseases reveal an ambiguous role of the compounds. Cancer-promoting but also anticancer effects were ascribed to methylglyoxal. Further work is still needed to elucidate the reactions of DCs during intestinal digestion and pathophysiological effects of dietary DCs at doses taken up with food and in "real" food matrices in disease states such as diabetes, uremia, and cancer.

Model Studies on the Effect of Aldehyde Structure on Their Selective Trapping by Phenolic Compounds

The reaction among flavor-relevant saturated aldehydes (propanal, 2-methylpropanal, butanal, 2-methylbutanal, 3-methylbutanal, pentanal, hexanal, and glyoxal) and phenolic compounds (resorcinol, 2-methylresorcinol, 2,5-dimethylresorcinol, and orcinol) was studied both to identify and to characterize the formed carbonyl-phenol adducts and to understand the differences in the carbonyl-trapping abilities of phenolic compounds. The obtained results showed that carbonyl-trapping by phenolics is selective and that the formation of carbonyl-phenol adducts depends on the structures of both the phenol and aldehyde involved. In relation to the phenolic derivative, the presence of groups that increase the nucleophilicity of phenolic carbons will increase the carbonyl-trapping ability of these compounds. On the other hand, the presence of groups that increase the steric hindrance of these positions without affecting nucleophilicity will inhibit the reaction. Analogously, the presence of branching at position 2 of the aldehyde will also inhibit the reaction by steric hindrance. All of these results suggest that the addition of phenolics to foods may change food flavor not only because of their sensory properties but also because they can modify the ratio among food odorants by selective reaction of phenolics with determined carbonyl compounds.